Efficient management and use of railroad freight cars require up-to-date information on the location of the railroad vehicles while they are i transit. Millions of dollars have therefore been spent on programs for monitoring the locations of freight cars in this and other countries.
The location monitoring programs commonly used over the years rely on visual sightings by individuals stationed at key sites and on data extracted from bills of lading and other freight documents. Such programs for keeping track of railroad freight cars are inefficient and unreliable. Furthermore, they are not designed to keep track of locomotives and cabooses.
As a result, numerous railroad cars and locomotives are often lost in the sense that the railroad vehicle owners and shippers are not certain where their railroad vehicles are at any particular time. Considerable time and money are therefore expended in tracing misplaced railroad cars and locomotives and attending to other problems arising from inadequate data on the locations of railroad vehicles. To a lesser extent the same or similar problems arise in the use of motor vehicle fleets such as trailer trucks.
In an effort to overcome the forgoing problem, various automatic car identification systems have been proposed for monitoring the locations of vehicles. Such systems typically employ responders which are carried by the vehicles and which are operated by awayside interrogating station to convey a coded vehicle-identifying signal to the interrogating station. Representative teachings of this type of interrogating system are found in U.S. Pat. No. 3,090,042 which issued to R. A. Kleist et al. on May 14, 1963, U.S. Pat. No. 3,270,338 which issued to R. L. Waters on Aug. 30, 1966, U.S. Pat. No. 3,713,148 which issued to M. W. Cardullo on Jan. 23, 1973, U.S. Pat. No. 3,859,624 which issued to T. A. Kriofsky et al. on Jan. 7, 1975, U.S. Pat. No. 3,839,717 which issued to J. C. Paul on Oct. 1, 1974, U.S. Pat. No. 3,984,835 which issued to G. S. Kaplan et al. on Oct. 5, 1976, U.S. Pat. No. 4,075,332 which issued to H. A. Baldwin et al. on Feb. 21, 1978, U.S. Pat. No. 4,114,151 which issued to Phillip Denne, on Sept. 12, 1978, U.S. Pat. No. 4,390,880 which issued to B. Henoc on June 28, 1983 and an article entitled "Short-Range Radio-Telemetry For Electronic Identification, Using Modulated RF Backscatter" by Alfred Koelle et al., proceedings of IEEE, Aug., 1975, pages 1260-1261.
The systems disclosed in the foregoing patents and publication, as well as known commercially available car identification systems, have a common shortcoming in that they each fail to satisfy all of the basic requirements for practical use in identifying freight cars and other railroad vehicles. These requirements include:
1. A small, totally passive, low cost responder which is adapted to be mounted on a railroad vehicle and which does not require any local power-producing source of its own for operation;
2. An interrogation system which accurately and reliably identifies railroad vehicles travelling over a wide range of speed extending from very low speeds up to relatively high speeds of about 100 mph;
3. An interrogation system in which none of the signal emissions requires an FCC license or other FCC approval;
4. An interrogation system having a suitable interrogation range in which sufficient power is delivered to the passive responder to enable the responder to redundantly emit an identification code to the interrogation station;
5. Built-in equipment for selectively testing the operability of the interrogating station;
6. Interrogating station and responder equipment designed to reliably and efficiently operate over long time periods without maintenance under all expected hostile environments, such as high and low ambient temperatures, rain, ice, snow, mechanical vibration and shock and the presence of chemicals or other deleterious materials which are hauled by freight cars;
7. An interrogation system which is capable of optionally collecting and recording information other than vehicle identifications, such as the speed and direction of the moving railroad vehicle, and the time and date when the information was acquired;
8. An interrogation system which produces a "clean list," that is, one which results in the identification of all vehicles;
9. An interrogation system which senses defective targets and which additionally distinguishes defective targets from the presence of passing railroad vehicles which are not equipped with targets or other responders; and
10. A target which is capable of being encoded in the field and which is also capable of having its stored information verified in the field.
Another problem with shipping freight by railroad involves the physical handling of waybills. According to the present-day practice, the waybills are typically hand carried by the train conductors and must be transferred by yardmen to the appropriate conductor at switching yards between the origin and destination points of the shipments, thus consuming time and labor.